Random drug testing in schools has cut the number of teenager users and should be considered by headteachers across the country, Ruth Kelly, the education secretary, said yesterday.

The Abbey school in Faversham, Kent, has been randomly testing pupils for illegal drugs since January 2005.

Speaking at the NASUWT conference in Birmingham, Ms Kelly told delegates the school had seen a marked improvement in performance since the scheme started and said she would welcome other schools adopting a similar scheme.

"Drugs is ... an issue which is not going away in schools," she said. "I was looking at the evidence from the Abbey school the other day where they have tried random drug testing and found that a hugely effective way of creating peer pressure against taking drugs in school."

The Abbey school has seen GCSE exam results improve significantly after introducing random testing. The school selects 20 pupils by computer each week who then take the tests, during which they are swabbed by specially trained staff.

The samples are sent off to a laboratory where they are checked for traces of drugs such as cannabis, cocaine and ecstasy.

Yesterday Peter Walker, the headteacher who introduced the scheme, said the government's support was "very important". More than 500 pupils had been tested and only one had proved positive. "The school has had the best 18 months in its history and its best exam results," he said. Tests had given pupils a reason not to take drugs.

Ms Kelly was speaking after delegates demanded action to tackle violent and disruptive pupils. The motion called on local authorities to provide more specialist units. Joy Higgins, from Chelmsford, Essex, said that even when unruly pupils were thrown out of school, they could be reinstated on appeal. She was not against the right to appeal but criticised the independent appeals panels, which she said often overturned sensible decisions.

One member of staff was struck on the back of the head by a rugby ball. The pupil was excluded but allowed back on appeal. "This sent a message to pupils that they had a charter for violence." Three days later there was "a copycat attack" on another member of staff, she said.

Ms Kelly was met with laughter when she argued that behaviour was generally improving. But there was applause when she said: "It only takes a few pupils engaged in low level disruption to make life a misery for pupils and teachers. That means we have to do something about it."

The union welcomed the government's plans to give teachers a clear legal right to discipline pupils and confiscate inappropriate items such as mobile phones.

Delegates at the Association of Teachers and Lecturers conference warned of an explosion in "cyber-bullying" and abuse via mobile phones among pupils.

Adrian Petty, a team leader at a Hertfordshire school, said mobiles had changed the culture of bullying. He spent hours each week reading emails and messages left on mobile phones. A survey of 800 ATL members found 71% had considered leaving teaching because of poor discipline, delegates heard.